1. Field of the Invention
This invention relates to a lens device and an image pickup apparatus adapted for use in lens-interchangeable type video cameras or the like.
2. Description of Related Art
The resent advancement of video apparatuses such as video cameras or the like has been conspicuous. These apparatuses are being arranged to have high performance capabilities and diverse functions. In the case of the video cameras, for example, they have come to be arranged to permit use of interchangeable lenses for the purpose of diversifying their functions and obtaining a higher image quality.
FIG. 1 shows, in a block diagram, the conventional arrangement of a lens-interchangeable type electronic camera adapted for a video camera.
Referring to FIG. 1, a lens unit 816 is arranged to have a variable magnification. A camera body 817 is arranged to permit the lens unit 816 to be mounted thereon. In the lens unit 816, a variator lens 802 and a compensator lens 803 are mechanically connected by a cam. When a magnification varying action is performed either manually or by means of a motor, the variator lens 802 and the compensator lens 803 move together. The variator lens 802 and the compensator lens 803 jointly form a zooming lens. In the lens system of the lens unit 816, a front lens is arranged to be a focusing lens 801. The focus of the lens system is adjusted by moving the focusing lens 801 along the optical axis. Light passing through these lenses is imaged on an image pickup plane of an image sensor 804 which is composed of a CCD or the like and is disposed within the camera body 817. The image thus formed is photo-electrically converted into an electrical signal and is outputted as a video signal. The video signal is supplied to a CDS/AGC (correlated double sampling/automatic gain control) circuit 805 to be sampled and held and amplified to a predetermined level. The amplified video signal is converted into digital video data by an A/D converter 806. The digital video data is supplied to a camera signal processing circuit 819 to be converted into a standard television signal. The digital video signal is supplied also to a band-pass filter (hereinafter referred to as BPF) 807.
At the BPF 807, a high frequency component of the video signal is extracted from the video signal. The output of the BPF 807 is supplied to a gate circuit 808 to extract therefrom only a signal part corresponding to a focus detecting area set within an image plane. The signal extracted is supplied to a peak hold circuit 809 to be peak-held at intervals synchronous with a period which is an integer times as much as the period of a vertical synchronizing signal. An AF (automatic focusing) evaluation value is obtained by this peak holding action. The AF evaluation value is taken in a microcomputer 810 which is disposed within the camera body 817. If the operated state of an AF/MF (automatic focusing/manual focusing) selection switch 823 indicates an AF mode, the camera-body microcomputer 810 decides a focusing speed corresponding to the degree of focusing and a motor driving direction for increasing the AF evaluation value. Information on the driving speed and the driving direction of a focus motor 813 is then sent from the camera-body microcomputer 810 to a microcomputer 811 which is disposed within the lens unit 816. In the event of the MF mode, the camera-body microcomputer 810 sends an instruction to the lens microcomputer 811 to stop the focus motor 813. In accordance with the instruction of the camera-body microcomputer 810, the lens microcomputer 811 makes focus adjustment by causing a motor driver 812 to drive the focus motor 813 in such a way as to move the focusing lens 801 along the optical axis.
Further, according to the operated state of a zoom switch 818, the camera-body microcomputer 810 decides the driving direction and the driving speed of the zooming lens (802 and 803) and sends information on the driving direction and speed to the lens microcomputer 811 to cause the zooming lens (802 and 803) to be driven accordingly by a zoom motor 815 through a zoom motor driver 814 disposed within the lens unit 816. The camera body 817 is arranged to permit the lens unit 816 to be detached therefrom and replaced with another lens unit, so that a photographable range of the video camera can be broadened.
For the purpose of attaining reduction in size and also making it possible to take a shot of an object located immediately in front of the camera, some of lens-integrated cameras designed for general consumers has come to be arranged to store the movement loci of a compensator lens beforehand in a microcomputer as lens cam data, instead of the above-stated arrangement of mechanically interconnecting the compensator lens 803 and the variator lens 802, to drive the compensator lens according to the lens cam data and to adjust focus also by means of the compensator lens. That arrangement is called an inner-focus type lens arrangement and has become popular. The advantages of the inner-focus type lens lie in that it is not expensive and permits system simplification and reduction in size and weight of the lens barrel.
FIG. 2 schematically shows the arrangement of the conventional inner-focus type lens system mentioned above. Referring to FIG. 2, a first lens group 901 is fixed. A second lens group 902 is arranged to be used for varying the magnification of the lens system. Reference numeral 903 denotes an iris. A third lens group 904 is fixed. A fourth lens group 905 is a focusing lens which is arranged to have a focus adjusting function and another function of compensating for a shift of a focal plane caused by a magnification varying action. Reference numeral 906 denotes an image pickup plane. In the lens system illustrated, the focusing lens 905 is arranged, as well known, to perform both the compensating function and the focus adjusting function. Therefore, even when the lens system remains at one and the same focal length, the focusing position of the focusing lens 905 relative to the image pickup plane 906 varies with the object distance, i.e., a distance to a shooting object. When the object distance changes at each focal length, the positions of the focusing lens 905 at which an in-focus state is obtainable on the image pickup plane 906 become as continuously plotted on a graph in FIG. 3. While a magnification varying action is in process, one of the loci of the focusing positions of the focusing lens 905 as shown in FIG. 3 is selected according to the object distance. A zooming action can be accomplished without blurring an image, by moving the focusing lens 905 according to the locus thus selected.
In the case of the front-lens focus type lens system shown in FIG. 1, the compensator lens is arranged independently of the variator lens, and the variator lens and the compensator lens are interconnected by means of a mechanical cam ring. Therefore, with the focal length of the lens system arranged to be manually variable by a manual zooming knob provided on the cam ring, the cam ring can be caused to rotate following the manual zooming knob to let the variator lens and the compensator lens move along the cam groove of the cam ring, at whatever fast speeds the knob may be moved. Therefore, the focal length can be varied as desired without causing any blur as long as the focusing lens of the lens system is in focus.
In controlling the inner-focus type lens system which is arranged as shown in FIG. 2, on the other hand, information on a plurality of lens-position loci which are as shown in FIG. 3 is stored in any suitable form, i.e., in the form of the loci or in the form of functions with the lens positions used as variables. Then, a suitable locus is selected according to the position of the focusing lens and that of the variator lens, and a zooming action is carried out by tracing the selected locus in general.
Further, in reading the position of the focusing lens relative to that of the variator lens for lens control, each lens position must be read out with a certain degree of reading accuracy. Particularly, in a case where the variator lens is moving at a constant or approximately constant speed, the inclination of the locus of the focusing lens is incessantly caused to vary by variations in focal length, as shown in FIG. 3. The varying inclination of the locus indicates that the moving speed and the moving direction of the focusing lens are incessantly varying. In other words, an actuator provided for the focusing lens must be arranged to accurately and speedily respond between 1 Hz and several hundred Hz.
To meet the above-stated requirement, it is a general tendency to employ a stepping motor as an actuator for the focusing lens of an inner-focus lens system. A stepping motor rotates perfectly in synchronism with stepping pulses outputted from a lens controlling microcomputer or the like. Since its stepping angle per pulse is constant, the use of a stepping motor ensures a high speed response, an adequate stopping accuracy and an adequate positional accuracy. Further, the use of a stepping motor permits use of the stepping pulses as an increment type encoder without recourse to any additional position encoder.
In a case where a magnification varying action is desired to be performed while retaining an in-focus state by means of a stepping motor as mentioned above, it is necessary to store beforehand, at a microcomputer or the like, information on the loci of lens positions which are as shown in FIG. 3 either in the form of loci as they are or in some other suitable form such as functions with the lens positions used as variables, to read the information on an applicable locus according to the position or the moving speed of the variator lens, and to cause the focusing lens to be moved according to the information.
FIG. 4 shows by way of example a known method for tracking (tracing) a locus. In FIG. 4, reference symbols Z0, Z1, Z2, - - - and Z6 denote positions of the variator lens. Symbols a0, a1, a2, - - - and a6 and symbols b0, b1, b2, - - - and b6 denote points forming representative loci stored within a microcomputer. Further, symbols p0, p1, p2, - - - and p6 denote points forming a locus computed oh the basis of the above-stated two loci according to the following formula:
xe2x80x83p(n+1)=|p(n)xe2x88x92a(n)|/|b(n)xe2x88x92a(n)|*|b(n+1)xe2x88x92a(n+1)|+a(n+1)xe2x80x83xe2x80x83(1)
In accordance with the formula (1), in a case where the focusing lens is located at the point p0 as shown in FIG. 4, for example, a ratio in which the point p0 internally divides a line segment b0-a0 is obtained. Then, a point which internally divides a line segment b1-a1 according to the ratio thus obtained is assumed to be the point p1. A moving speed of the focusing lens at which an in-focus state is retainable can be obtained from a positional difference between the points p1 and p0 and a period of time required in moving the variator lens from the position Z0 to the position Z1.
In a case where the stopping positions of the variator lens are not limited to boundaries represented by the data of representative loci stored, the lens position control is performed in the following manner. FIG. 5 is a diagram for explaining a method of making interpolation in the direction of the variator lens position. In this case, a part of FIG. 4 is extracted and the variator lens is considered to be at any arbitrary position. In FIG. 5, the position of the focusing lens is shown on the ordinate axis and that of the variator lens is shown on the abscissa axis. The positions on the representative loci of the focusing lens stored in the lens control microcomputer relative to the variator lens positions are set as follows. The positions of the focusing lens for the variator lens positions Z0, Z1, - - - , Zkxe2x88x921, Zk, - - - , Zn are set for different object distances as follows:
a0, a1, - - - , akxe2x88x921, ak, - - - , an,
and
b0, b1, - - - , bkxe2x88x921, bk, - - - , bn.
In a case where the variator lens position is located at a point Zx. which is not on a zooming boundary and the focusing lens position is at a point Px, focusing lens positions ax and bx are obtained respectively in accordance with the following formulas (2) and (3):
ax=akxe2x88x92(Zkxe2x88x92Zx)*(akxe2x88x92akxe2x88x921)/(Zkxe2x88x92Zkxe2x88x921)xe2x80x83xe2x80x83(2)
bx=bkxe2x88x92(Zkxe2x88x92Zx)*(bkxe2x88x92bkxe2x88x921)/(Zkxe2x88x92Zkxe2x88x921)xe2x80x83xe2x80x83(3)
In other words, of the four representative locus data stored, i.e., ak, akxe2x88x921, bk and bkxe2x88x921 shown in FIG. 5, the data for one and the same object distance are divided internally according to an internal ratio determined by the current variator lens position and two zooming boundary positions (for example, Zk and Zkxe2x88x921 in FIG. 5) before and after the current variator lens position. The focusing lens positions ax and bx can be obtained by carrying out this process. Then, positions Pk and Pkxe2x88x921 can be obtained by obtaining an internal ratio from the lens positions ax, Px and bx, and by internally dividing data which are included in the four representative data in store (ak, akxe2x88x921, bk and bkxe2x88x921 in FIG. 5) and are for one and the same focal length in accordance with the internal ratio thus obtained, as explained in the formula (1). Then, in zooming from a wide-angle end position to a telephoto end position, a focusing lens moving speed which is required for retaining an in-focus state can be found from a positional difference between the tracking focusing position Pk and the current focusing position Px and a period of time required in moving the variator lens from the position Zx to the position Zk. Further, in zooming from the telephoto end position toward the wide-angle end position, a focusing lens moving speed required for retaining an in-focus state can be found from a positional difference between the tracking focusing position Pkxe2x88x921 and the current focusing position Px and a period of time required in moving the variator lens from the position Zx to the position Zkxe2x88x921.The known locus tracking (tracing) method is as described above.
While the kinds and arrangement of known zooming actions have been described above, there is another known method for attaining a zooming effect. This method is called xe2x80x9celectronic zoomingxe2x80x9d. In the electronic zooming, while the size of an image formed is constant, a range of the image actually outputted to a recording part or to an viewfinder can be gradually changed on an image forming plane. The advancement of various interpolating methods for video signals has come to make the electronic zooming up to two magnifications or thereabout practicable.
The electronic zooming of an interchangeable lens system is described by way of example below with reference again to FIG. 1. The camera signal processing circuit 819 shown in FIG. 1 is arranged to perform white-balance and aperture adjusting processes on a picked-up video image. A video signal processed by the camera signal processing circuit 819 is stored in a field memory 820. An interpolation circuit 821 is arranged to read the image in storage and to output a magnified signal obtained by interpolating the image between scanning lines and between picture elements to vertically and horizontally magnify the image read out. The magnified signal is sent back to the camera signal processing circuit 819 to be converted into the form of a standard TV signal. The standard TV signal thus converted is sent as a video signal to a recording system or a viewfinder system.
The interpolation circuit 821 is controlled by the camera-body microcomputer 810 in accordance with information on a magnifying rate obtained according to the operated state of the zoom switch 818. Assuming that the magnifying rate of the zooming lens is 12 magnifications and that of the electronic zooming is two magnifications, for example, a zooming effect of 24 magnifications can be obtained in all. In this case, when the zoom switch 818 is operated for zooming from the wide-angle end position toward the telephoto end position, a zooming action of connecting the electronic zooming is carried out after the telephoto end position of the optical zooming, as shown in FIGS. 6(a), 6(b) and 6(c). The telephoto end position of the optical zooming is detected by the lens microcomputer 811. The information on the position of the zooming lens is sent from the lens microcomputer 811 to the camera-body microcomputer 810. Then, the camera-body microcomputer 810 decides whether or not the optical zooming is to be shifted to the electronic zooming.
In FIGS. 6(a) to 6(c), the operating time of the zoom switch 818 is shown on the abscissa axis. The ordinate axis shows the total magnifying rate in FIG. 6(a), the magnifying rate of the electronic zooming in FIG. 6(b) and the magnifying rate of the optical zooming in FIG. 6(c). While the electronic zooming is assumed to be arranged to vary the magnifying rate further after arrival of the variator lens at the telephoto end position, the arrangement may be changed to allow the change-over from the optical zooming to the electronic zooming to take place not only at the telephoto end position but also at some other positions in such a way as to have the electronic zooming overlap the optical zooming. Further, while all displacements shown in FIGS. 6(a) to 6(c) are arranged to linearly take place, the system is not limited to that arrangement.
However, in the case of the inner-focus type lens system which is as shown in FIG. 2 and is advantageous in terms of simplification and reduction in cost, size and weight, an attempt to make the lens system of this type into an interchangeable lens unit has encountered the following problem. Unlike the front-lens focus type lens system of FIG. 1, the mechanical arrangement of the lens system of FIG. 2 prevents a direct manual operation on the lens group. Therefore, in varying its magnification, it is possible only to adjust the angle of view by a power zooming action with a motor. This impairs the operability of the video camera. For example, in a case where the lens unit mounted on the camera body is large, a shooting operation is performed with the lens part held by one hand of the operator. Therefore, if no operation mechanism for adjustment of angle of view is provided on the lens part, the operator is compelled to detach his or her eye from a viewfinder to look for a zooming operation switch. In such a case, the video camera cannot be smoothly operated for shooting.
Further, for the interchangeable lens system, no known prior art has made a clear disclosure with respect to a zooming method, particularly a method for interlocking the optical zooming and the electronic zooming, to be applied to a case where an electronic zooming function is arranged on the side of the camera body. The absence of such a method has left the following problem to be solved. The variator lens group in the lens system might move toward the wide-angle end while the electronic zooming function remains in an on-state. Then, while it is possible to take a high quality picture at the same angle of view by combining an electronic magnifying rate with some other optical magnifying rate, the shooting operation might be carried out in a state of having a deteriorated picture quality with the electronic zooming function left in its on-state.
Further, the arrangement of the video camera having an AF/MF selection switch disposed on the side of the camera body has presented another problem that, in cases where shooting must be performed while holding the lens part, the location of the AF/MF selection switch makes the operation not easy. Particularly, where a lens system having manual-zooming and manual-focusing operation systems at the lens part is mounted on the camera body, the locations of the operation members of the lens system must be divided between the lens part and the camera part. As a result, a shooting operation by looking into a viewfinder becomes difficult. In such a case, some wrong switch either might be operated by mistake in search of the AF/MF selection switch or a shooting operation must be suspended in search of the correct switch. Besides, in such a case, adequate shooting might be prevented by shaking of the video camera.
It is an object of this invention to provide a lens control device and an image pickup apparatus which solve the above-stated problems and are arranged, without impairing their operability, to be capable of adequately carrying out a shooting operation with any type of lens unit mounted or at any angle of view.
It is another object of the invention to provide a lens device and an image pickup apparatus having an interchangeable lens system, wherein control over actions to be performed on the side of a camera body can be controlled from on the side of a lens unit.
To attain these objects, a lens control device arranged as a preferred embodiment of the invention comprises variator lens means for performing a magnification varying action, compensator lens means for correcting focus so as to retain an in-focus state during the magnification varying action, operation means operable by a user for causing the magnification varying action to be performed, and control means for controlling the magnification varying action by moving the variator lens means and the compensator lens means along an optical axis according to an operation of the operation means and according to a control signal supplied from an image pickup apparatus body.
An image pickup apparatus arranged as a preferred embodiment of the invention comprises a lens device and an image pickup apparatus body. The lens device comprises variator lens means for performing a magnification varying action, compensator lens means for correcting focus so as to retain an in-focus state during the magnification varying action, first operation means operable by a user for causing the magnification varying action to be performed, and first control means for controlling the magnification varying action by moving the variator lens means and the compensator lens means along an optical axis according to an operation of the first operation means and according to a control signal from the image pickup apparatus body. The image pickup apparatus body comprises image pickup means for obtaining an image signal by picking up an image of an object through the variator lens means and the compensator lens means, second operation means for causing the magnification varying action to be performed, and second control means for sending the control signal to the first control means according to an operation of the second operation means.
A lens device arranged as a preferred embodiment of the invention comprises focusing lens means, operation means operable by a user for permitting or inhibiting a focusing action, and control means for performing control to move the focusing lens means to an in-focus point according to an operation of the operation means and according to a control signal supplied from an image pickup apparatus body for permitting or inhibiting the focusing action.
An image pickup apparatus arranged as a preferred embodiment of the invention comprises a lens device and an image pickup apparatus body. The lens device comprises focusing lens means, first operation means operable by a user for permitting or inhibiting a focusing action, first control means for performing control to move the focusing lens means to an in-focus point according to an operation of the first operation means and according to a control signal supplied from the image pickup apparatus body for permitting or inhibiting the focusing action. The image pickup apparatus body comprises image pickup means for obtaining an image signal by picking up an image of an object through the focusing lens means, second operation means operable by the user for permitting or inhibiting the focusing action, and second control means for sending the control signal to the first control means according to an operation of the second operation means.
It is a further object of the invention to provide a lens control device and an image pickup apparatus which are arranged such that, with a lens device mounted on an image pickup apparatus body, a magnification varying action can be performed separately from operation control performed on the side of the image pickup apparatus body, by operating operation means provided on the side of the lens device.
It is a still further object of the invention to provide a lens control device and an image pickup apparatus which are arranged such that, with a lens device mounted on an image pickup apparatus body, starting and stopping of a focusing action can be controlled separately from operation control performed on the side of the image pickup apparatus body, by operating operation means provided on the side of the lens device.